None.
The present invention relates to semiconductor materials, and, in particular, relates to nitride materials, and more particularly relates to GaN.
The current substrates of choice for M-nitride electronic components are sapphire, lithium gallium oxide, silicon carbide or zinc oxide. M represents gallium, aluminum, indium, germanium, zinc and ternary combinations and alloys of the above such as zinc germanium and indium aluminum gallium. Sapphire is low in cost but has a lattice mismatch exceeding 12%. Lithium gallium oxide has a thermal expansion mismatch, crystal twinning problems, and the possibility of contaminating deposited films when used as a substrate. Silicon carbide has a close lattice match with the nitrides but it is expensive. The fact that SiC has a different crystal structure from the wurtzite crystal structure of the nitrides is believed to cause stacking faults in deposited films. Zinc oxide has the same wurtzite crystal structure as the metal nitrides but is also very expensive. Its limitation for use as a substrate is the inability to sustain high temperatures and its reaction with HCl and organometallics currently used in most deposition processes.
In the absence of methods for producing large metal nitride single crystals, growth of thick metal nitride films on alternative substrates (hetero-epitaxy) has been attempted as a means of producing large area substrates. A number of innovative schemes have been developed to overcome strain problems with thick epitaxial M-nitride layers (xe2x80x9cGallium Nitride Thick Films Grown by Hydride Vapor Phase Epitaxyxe2x80x9d, by R. J. Molnar et al., Proceedings, 1996 MRS Spring Meeting). However, additional expensive engineering steps required to grow adequate films for electronic devices make these processes undesirable.
The ideal choice for M-nitride epitaxy would be a substrate of the same material (homo-epitaxy) with an exact match of lattice parameter, crystal structure and thermal expansion coefficient. For this purpose, bulk growth of M-nitride material is intrinsically the most desirable approach to creating M-nitride substrates. Currently the only bulk growth of the nitride materials involves a very high pressure, (exceeding 20,000 atmospheres) and high temperature (above 1400xc2x0 C.) reaction of nitrogen and the metal of choice, which makes this a non-viable commercial process (xe2x80x9cThe Homoepitaxy of GaN by Metalorganic Vapor Phase Epitaxy using GaN Substratesxe2x80x9d, by T. Detchprohm et al., Journal of Crystal Growth 137 (1994) 170). A similar system was employed for growth of A/N crystals using high pressure (Growth of High Purity A/N Crystalsxe2x80x9d, by G. Slack et. al., Journal of Crystal Growth 34 (1976) 263). This is also a non-viable commercial process.
This invention provides a process and apparatus for producing products of M-nitride materials wherein M=gallium (GaN), aluminum (A/N), indium (InN), germanium (GeN), zinc (ZnN) and ternary nitrides and alloys such as zinc germanium nitride or indium aluminum gallium nitride. This process and apparatus produce either free-standing single crystals, or deposit layers on a substrate by epitaxial growth or polycrystalline deposition. Also high purity M-nitride powders may be synthesized.
The process uses an ammonium halide such as ammonium chloride, ammonium bromide or ammonium iodide and a metal to combine to form the M-nitride which deposits in a cooler region downstream from and/or immediately adjacent to the reaction area. High purity M-nitride can be nucleated from the vapor to form single crystals or deposited on a suitable substrate as a high density material. High purity M-nitride single crystals can be grown by the direct reaction of the halide with the M-metal in a range of sizes from a few micrometers to centimeters, depending on the growth conditions. The small sized crystals are recovered as high purity M-nitride powder while the larger crystals can be prepared as substrates for electronic devices or UV/blue/green emitting diodes and lasers. The deposited layers can be used as M-nitride substrates, or targets for pulsed laser deposition (PLD), or other systems requiring high density targets. The deposition process, and subsequent density of the resulting component, is controlled by the reaction medium and by adjusting the temperature of the ammonium halide in an area near but separate from the reaction zone. Thickness of deposition on the substrates by the same process involves placement of the substrates in a suitable area in the reaction chamber and may be further controlled by the use of nitrogen, nitrogen-hydrogen mixtures or other suitable controlling gas to facilitate uniform distribution of the layer.
Therefore, one object of the present invention is to provide an apparatus and process for producing products of M-nitride materials.
Another object of the present invention is to provide an apparatus and process for producing products of GaN.
Another object of the present invention is to provide an apparatus and process for producing products of M-nitride materials with variable reactor conditions from low pressures to above atmospheric and temperature ranges from a few hundred degrees centigrade to well over one thousand degrees centigrade.
Another object of the present invention is to provide an apparatus and process for producing products of M-nitride materials such as free-standing single crystals and layers on a substrate.
Another object of the present invention is to provide an apparatus and process for producing products of M-nitrides such as free-standing single crystals and layers on a substrate including powders thereof.
Another object of the present invention is to provide an apparatus and process for producing products of M-nitride materials for use as UV/blue/green LEDs, lasers and UV detectors, for example.
Another object of the present invention is to provide an apparatus and process for producing products of M-nitride materials which use an ammonium halide and a metal to combine to form the materials of interest.
Another object of the present invention is to provide an apparatus and process for producing products of M-nitride materials such as small single crystals for use as powders, large single crystals for use as component substrates, deposited layers for use as M-nitride substrates, targets for pulsed laser deposition, or other processes requiring high density materials with low O2 content.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the pertinent art from the following detailed description of a preferred embodiment of the invention and the related drawings.